Riken and Da Vinci Co Ltd, whose headquarters are located in Nara Prefecture, Japan, invented a "cogeneration system" that collects the thermal energy of sunlight including lights from the rising and setting suns with Fresnel lenses and heats up water stored in a heat storage tank to generate electricity and supply hot water.
The system heats up water by using the thermal energy of sunlight and a heat exchanger and stores the heat so that the heat can be used for generating electricity and supplying hot water. By three-dimensionally combining Fresnel lenses that have concentric slits, it became possible to efficiently collect energy regardless of the angle of sunlight from sunrise to sunset.
A Fresnel lens can efficiently converge light even when its thickness is small. The lens employed for the system is based on a telephoto lens being developed for observing ultrahigh energy cosmic rays. Therefore, it has a high transparency, and its roughness is as low as 20nm.
This lens was attached to the top and lateral sides of a cubic unit. And this is called "Fresnel Sun House."
Inside the cubic unit, there is an inverted T-shaped heat exchanger that is made of aluminum alloy and receives light converged by the Fresnel lenses so that heat energy can be efficiently collected no matter which lens sunlight passes through. A heat storage tank is located below the heat exchanger, and the water heated in the tank is supplied to the "rotary heat engine" developed by Da Vinci for power generation.
The rotary heat engine is rotated by evaporating an alternative for chlorofluorocarbon, which is a thermal catalyst, etc. Because rotational energy is generated by the change of the cylinder's volume, it is possible to achieve a high power generation efficiency even with a low pressure from a low-temperature heat source. Specifically, it can be used even with a temperature of about 40°C.